The present invention relates to a vacuum distillation system wherein feed is heated by indirect heat exchange in tubes of increasing diameter and through a conduit of gradually increasing diameter passed to a vacuum distillation column. The system comprises a vacuum distillation column having a column inlet, a bottom outlet and a top outlet, a furnace provided with a heat-exchange tube having a tube inlet and a tube outlet, and a connecting conduit provided with an inlet end connected to the tube outlet and an outlet end which is in fluid communication with the column inlet.
Such a vacuum distillation system may be used to fractionate a hydrocarbon-containing feed which feed is sometimes referred to as long residue. During normal operation the absolute pressure in the vacuum distillation column is maintained between 650 and 5 200 Pa. Liquid feed passing through the heat-exchange tube in the furnace is partly vaporized and the partly vaporized feed i supplied through the connecting conduit to the column inlet at a temperature of between 380.degree. and 425.degree. C.
It is an object of the present invention to provide a vacuum distillation device which allows vaporization of a major part of the feed upstream the column inlet.